Retaining Wall Advice

Hi Everyone

First of all, thanks for all the great reading (long time reader, first time poster)

I would really appreciate some advice on how to proceed with my retaining wall - in particular my messed up corner post.

Basically I am building a retaining wall in an L shape, which will then be filled, in order to extend our lawn on our sloping section. The wall is approx 9m x 10m ranging in height from starts 1m - 1.4m (at the corner) - 0.2m on the opposite end. Purpose is purely for making our usable flat lawn bigger and does not support a driveway, structures etc.

I have just had all the holes drilled by a small digger, but after sitting back and calculating the wood I require I realise I have made a mistake in marking out the holes in particular the corner post which makes up the L shape (and which is also the lowest point /will be the highest point from the existing ground level once filled)

I know that I should have started with the corner post and worked back from there, meaning post 1 would be much closer to the corner post (marked 2)

Materials being used - 200 diameter H5 rounds to be set in 400 diameter holes filled with 20mPa concrete & 150x50 H4 tongue & groove retaining boards fixed by 150mm galv nails to the inside of the posts. The inside will then be filled, (pushing the boards against the posts) & compacted (driven over by digger) with a mixture of discarded concrete pieces, clay & dirt -and finally a layer of topsoil

Drawings attached (hope they make sense) of the current situation and a few solutions as to how to proceed, but wanting any other ideas or recommendations on the proper way to go about it.
Or am I just stressing & worrying and it should be ok considering I have tried to over spec the wall in the first place? (e.g. holes are the height of poles out of the ground + 200mm)

110mm perforated drainage pipe + scoria + geotextile fabric will be used along both lengths of wall, joining at the corner discussed and will then carry on further past the wall to meet up with existing drainage pipe

Plan is to then build a 1m high fence on top of this (not sure if I should bold the fence posts to the retaining wall or set fence posts in concrete in/on the newly filled material?

Thanks

Pics won't load for me.
Retaining walls over 1 meter ought to be engineered. A specialist will analyze the soil, wind, (VERY important! Wind on the fence can add a LOT more stress on the wall) water and other factors and tell you post size, spacing, material, concrete specs, drainage materials and methods.
As a designer I will suggest these factors to the client, and bid the job "subject to engineering"
Here is how I would build a retaining wall 1.4 m high with a fence on top: minimum post size: 15 cm x 15 cm x 2.8m, wood rated for direct burial ( ground contact) in hole 35cm diameter minimum with concrete.
Distance between posts 1.3m max. Even stronger would be steel I beams as posts. Alternate posts extended to become fence posts. Horizontals of the retaining wall 8cm min thickness, 10 cm better, also treated for ground contact. Gap the horizontals a few mm to allow some water to weep out.
Drainage needs should similarly be assessed, and since you are planning a lawn on top maximum drainage and protection for the wall since lawns are high water use. Products that I specify might not be available under that name, but google Delta Drain, see if that is available to you. To fix mistaken hole fill, compacting as you fill, then drill new holes. Proper compaction of the fill is very important.

How

OK, pictures loaded.
You are right, that is quite a problem.

Best solution:
Fill and compact the nearest holes and re-drill them. If you fill the holes about 10cm at a time and compact a LOT then it will be almost as if there were never holes there. Then the new holes will have the full support of the soil around them.

Put 2 in the corner, they may run into each other, but one post will support one part of the L, the other post will support the other part of the L. Measure from where the lumber comes together and hold the posts back perhaps 20-30cm from the end.

I would not risk any sort of 'fix it' solution that does not fully support both wings of the wall.

The wall is too high, and with a fence on top this is a wall that will be subject to a lot of stress. If there is any way of holding the fence back at least 2 meters from the wall that would remove that part of the stress from the system.

Another idea:

In the second picture you have colored the walls. I am looking at the tan colored wall.
In both pictures you have drawn one wall continuing beyond the end of the other.
Do that.

Bolt to the tan colored wall a square post on the outside of the other wall, right in the corner. Almost where you have drawn hole no. 3.
The bolts should go all the way through post no. 1, too, if the line up is as drawn.
The square post will not go into the ground. It will be 1.4m long.
The square post should be rated for ground contact.

I do not think this is not as good a solution as redigging the holes.

Fence attachment:
a) Separate structure, bolt the fence posts to the retaining wall posts would give you the option of taking down the fence and replacing it if needed. You could use smaller lumber on the fence, too.

b) Extending the retaining wall posts up to support the fence means that the fence would look heavier, because it has those large posts. That might be OK, if you like the look. It is also structurally stronger. Every time you put 2 pieces of wood next to each other you are creating a damp area where rot can set in. You would not have to extend every post, of course. As few as 1 post out of 3 might be plenty, or a stronger fence by using every other post.

Is there any way you could hire a stone waller as we call them here, it's a dying trade now here any-rate, we had to repair old walls i4-8 feet high n our huge garden, as I love properly build structured made from stone and properly engineered as Diana stated, then the cheapest way for us to do it and in agreement with the stone worker, WE did the labouring and the stone mason did the building.
We were surprised at the skills needed to cut the stone, select the right size of stones starting with really large wide ones for the footings and gathering small stores for back filling as the walls we had were retaining walls broken by tree roots and water / frost.

It was so worth it and we learned a lot BUT NOT ready to tackle a job ourselves, it really is a skilled job and such a thing of beauty when completed.
Hope this gives another slant on wall construction.
Best of luck.
WeeNel.

Diana_K - Thank you very much for your replies, you seem to be thinking about this and the solutions in a similar fashion to me (coming up with a solution, examining it's merits and then also proposing another to see how it stacks up!)

I can't extend the posts up to double as fence posts as these have already been ordered + as you mention it would look a bit out of place, these massive posts for a small fence.

"If there is any way of holding the fence back at least 2 meters from the wall that would remove that part of the stress from the system." I am not sure what you mean by this?

I have come up with the same solution you proposed regarding attaching a square post to the post #2 which the boards from the second wall can attach to - see my drawing attached to see if this is what you had in mind. I am thinking a piece of wood treated to ground contact, approx size 200x75 (8x3?) 1.4m high. Attached through the tan boards and through post #2 with m16 coach bolts 350mm length, spaced every every 30cm or so?

WeeNel - I would very much love a stone wall - we have quite a lot of volcanic rock in my city so there are a few stone masons which operate - however it is pretty much the most expensive option for building a wall. - I have tried to look into this as an option for the front of our property but costs really are astronomical - I am still weighing up to tackle the job myself - but might need to hire a stone mason to do the foundation and start off the first couple levels and I go from there - we'll see.